1. Field of the Invention
The present invention relates to an improved stonewashing stone and to methods for making and using a preferred plastic stone. More specifically, the present invention is directed to a durable plastic stone useful in a garment stonewashing process having a density and abrasiveness approximating that of pumice stone.
2. Description of the Background
In recent years, fabric having an aged appearance has experienced a significant increase in value. An exemplary fabric processed to have an aged appearance is denim. Various methods have been developed for commercial processing of denim to produce this effect. Typically, these commercial processes involve abrading the fabric with a pumice stone, either natural or manmade from pumice granules.
The stonewashing process consists of several distinct operations that occur after loading the fabric or garment into a washing machine. The first operation is typically that of desizing. Sizing, or unwanted filling in the fabric, is removed with desizing chemicals. Desizing agents such as amylase enzyme, caustic soda and peroxide, or other desizing agents are added to the bath for this purpose. The desizing agents break down the sizing that often includes waxes or starches. If not for the desizing step, the sizing might come between the cotton fibers to insulate the cotton fibers from chemicals used in subsequent steps of the stonewashing process.
The second step is normally the abrading step that gives the garment an aged appearance. Over time, the mechanical action from even a standard washing machine will abrade the fabric sufficiently to produce an aged appearance. However, for commercial feasibility in producing the aged look, normal washing requires too much energy and time.
It has been known for some time that the use of pumice rock is especially effective for abrading denim. It produces a substantially uniform aged look and speeds up the process to save time and energy. The pumice rock and the garments tumble against each other in the rotating washing cylinder. Chemical agents, such as cellulase enzyme, are also presently used for producing the aged look. Often the steps of washing, tumbling with pumice rock, and adding enzymes are combined. The desired aged appearance effect is thereby obtained at a relatively low cost.
A conventional step in the stonewashing process produces the preferred shade, contrast, and feel. This step frequently utilizes a series of applications of chemicals, such as chlorine bleach, oxygen bleach, and optical brighteners, to produce the desired characteristics.
While the use of pumice stone has been effective in the stonewashing process, pumice stone has several disadvantages. During the abrading process, pumice deteriorates rather quickly to produce sand and grit, i.e., pumice has a high attrition rate. The pumice grit also attacks the seals and bearings of the abrading or washing cylinders, causing increased downtime. Accumulating pumice in drains and sumps acts to create a significant odor that permeates the workplace, and the waste is costly to dispose of. Pumice usage indirectly causes environmental concerns because the mining of pumice stone typically damages the landscape. Transportation, mining, and storage costs for the pumice add significant costs to the stonewashing process.
Due to the problems associated with pumice rock in the stonewashing process, other materials have been tested for use in place of pumice. These materials include broken stone, nuggets of metal, cement blocks, ceramic briquets, and hard plastics including polypropylene. While these materials have, in some instances, reduced attrition rates compared to pumice rock, they typically have other disadvantages. For instance, most of these products lack the desired density to produce uniform abrasion. Most of these materials produce damaging holes in the garments. The lighter materials, such as polypropylene briquets, do not produce significant abrasion within a reasonable time period, thereby increasing energy costs and reducing the efficiency of a stonewashing facility.
Consequently, a need exists for improvements in the stonewashing process. Efficiencies of time and energy require improvement in the abrading step that presently uses pumice stone. The output quality of the abrading process using pumice stone should be maintained, while damage to the environment should be limited. Working conditions at fabric stonewashing facilities may be improved, and inventory and shipping costs for the abrading material need to be lowered. Those skilled in the art have long sought and will appreciate the novel features of the present invention that solves most if not all of these problems.